The candidate for this Clinical Investigator Award, Dr. Robert Buras, is a surgical oncologist with six years of clinical training and four years of research training. He currently devotes 40% of his effort to research and 60% to clinical and teaching activities. This award would enable Dr. Buras to increase his research effort from 40% to 80%. He would use this opportunity to study the mechanisms through which 1,25-(OH)2-vitamin D3(1,25-D2) and vitamin D analogs inhibit breast cancer cell growth. The proposed studies will analyze differential gene expression in MCF-7 breast cancer cells treated with 1,25-D3 and Ro24-5531. MCF-7 cells express vitamin D receptors (vDR) and demonstrate significant growth inhibition by 10-8M 1,25-D3 or Ro24-5531. Ro24-5531, a non-hypercalcemic vitamin D analog, decreases the incidence of breast tumors in a rat carcinogenesis model. MCF-7 cells will be grown in standard media, in media depleted of vitamin D and in media supplemented with 1,25-D3 or Ro24-5531. Differential gene expression will be analyzed by PCR-based differential display. Differentially-expressed genes will be cloned, sequenced and analyzed for homology with known proteins or functional groups to determine possible significance to the antiproliferative effect of 1,25-D3 and vitamin D analogs. The cellular distribution and timing of expression of regulated gene products will be studied using anti- protein antibodies. The effects of regulated proteins on cell growth, differentiation, invasiveness and progression through the cell cycle will be studied. The promoter region of genes which mediate the antiproliferative effects of 1,25-D3 or Ro24-5531 will be analyzed to determined mechanisms of transcriptional regulation. These studies will improve our understanding of the mechanisms through which 1,25-D3 and Ro24-5531 regulate cancer cell growth and differentiation. This insight may suggest new strategies for the prevention and treatment of breast cancer. Dr. Buras' research will be conducted under the direction of Dr. Marc Lippman, Director of the Lumbardi Cancer Center (LCC). The LCC has the facilities necessary for Dr. Buras to successfully complete this research. Numerous senior staff of the LCC, including many established breast cancer researchers, will be available to Dr. Buras for consultation. At the conclusion of this award, Dr. Buras will have acquired the experience and critical thinking necessary to direct an independent research program.